Fortification

This single timing decision separates Port from Fino sherry.

Adding spirit during fermentation raises the alcohol above what yeast can survive, killing it and leaving the remaining sugar in the wine. That produces Port, Madeira, Vins Doux Naturels and Moscatel.

Adding spirit after fermentation has finished leaves nothing to preserve, so the wine stays dry. That produces Fino, Manzanilla, Amontillado and Oloroso.

Fortified wine keeps far longer after opening than table wine, because the alcohol inhibits spoilage — though how long varies enormously by style.

Fortification means adding neutral grape spirit to wine. When and how much decide everything about the result.

Added during fermentation, the spirit raises the alcohol past what yeast can survive — around 15% — and stops the process, leaving unfermented sugar behind. Port, Banyuls, Maury and the vins doux naturels are all made this way, which is why they are sweet.

Added after fermentation has finished, there is no sugar left to preserve and the wine stays dry. Fino and Manzanilla Sherry are fortified this way, to around 15%, which is exactly the level at which the flor yeast can survive and grow.

Sherry then splits on that point. Wines fortified to 15% develop under a protective film of flor and stay pale and saline; those fortified to 17% or more kill the flor and age oxidatively, turning amber and nutty. One decision at the start produces Fino or Oloroso.

The higher alcohol makes fortified wine far more stable once opened. An oxidatively aged style has already had its oxygen exposure and will keep for weeks, where a Vintage Port — aged reductively in bottle — behaves like a table wine and should be finished within days.